(a) Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display.
(b) Description of the Related Art
Generally, a liquid crystal display (LCD) includes upper and lower panels provided with field-generating electrodes and a liquid crystal (LC) layer interposed therebetween. The upper and the lower panels are combined with a sealant printed along periphery thereof and enclosing the LC layer and they are spaced apart with a gap supported by a plurality of spacers.
The LCD applies voltages to the field-generating electrodes to generate an electric field in the LC layer having a dielectric anisotropy and controls the magnitude of the voltages applied to the electrodes to control the strength of the electric field, thereby controlling the transmittance of light passing through the LC layer to display images.
One of the techniques of filling the liquid crystal in the gap between the two panels is so called drop filling. The drop filling defines a filling area enclosed by a sealant having a closed-loop shape on one of the two panels and drops the liquid crystal in the filling area. The two panels are assembled in a vacuum state and the sealant is hardened. An important issue is to make the thickness of the liquid crystal kept constant without any void in the filling area of the panel for obtaining a uniform cell gap.
The uniformity of the cell gap is determined by the uniformity and the amount of a liquid crystal coated in the filling area on the panel. In order to improve the uniformity of the cell gap and to remove the voids in the liquid crystal layer as well as to match the process time in a manufacturing line, it is preferable to shorten the tact time by using one drop filling that has an advantage of filling accurate amount of the liquid crystal. It is because although each drop causes a minute deviation, the accumulation of the minute deviations for several drops causes significant errors.
However, the one drop filling has a disadvantage of the prevention of voids. The voids are mainly formed by different diffusion distances when diffusing the dropped liquid crystal. In particular, the voids are more probable to be generated near the corners of the panels. The difference in the diffusion distances is resulted from several causes such as the rectangular shapes of the panels, the difference in the materials of the diffusion surfaces, the evenness of the diffusion surfaces, existence of the sealant, and so on.
The probability of the generation of the voids depends on the characteristics of the liquid crystal and the modes of the LCD. For example, a twisted nematic (TN) mode LCD, an in-plane-switching (IPS) mode LCD, and an optically compensated birefringent (OCB) mode LCD, which employ homogeneous (or horizontal) liquid crystal alignment, has less probability of the void generation than a vertically aligned (VA) mode LCD employing homeotropic (or vertical) liquid crystal alignment. The voids generated in the display area is called AUA (active unfilled area), while the voids generated near the sealant is called SUA (surface unfilled area).